Conventionally, it is well known that an injector may include a needle, a body, a back pressure chamber, an inflow passage, an outflow passage, and a drive unit, as will be explained. The needle is a valve body which opens and closes an injection hole that injects fuel. The body is cylindrical and houses the needle therein. Further, the body includes the injection hole. The back pressure chamber is provided for exerting a fuel back pressure in the direction of closing the injection hole. The inflow passage is provided to allow fuel to flow into the back pressure chamber, such that high pressure fuel from a supply pump is always allowed to flow from the inflow passage into the back pressure chamber. The outflow passage is provided to allow fuel to flow out from the back pressure chamber. The drive unit opens or closes the outflow passage based on a control signal from a controller, and thereby increases or decreases the back pressure to control the opening and closing of the injection hole via the needle.
However, according to such an injector, when the outflow passage is opened, a connection between the inflow passage and the outflow passage is maintained and high pressure fuel is continuously expended. As a result, the load on the supply pump may be significant. Further, a large amount of force may be necessary to close the outflow passage, and thus the physical size of the drive unit may need to be large as well.
In this regard, regarding the injector, it is known that a moveable plate may be disposed within the back pressure chamber in a floating state (for example, refer to Patent Literature 1). According to the configuration of Patent Literature 1, when the outflow passage is opened, the movable plate is moved due to a pressure difference, and the opening to the inflow passage is closed. For this reason, when the outflow passage is opened, a connection between the inflow passage and the outflow passage is blocked. As a result, high pressure fuel is not expended and the load on the supply pump may be reduced. Further, a large amount of power may not be needed to close the outflow passage, and so the physical size of the drive unit may be reduced.
With the configuration of Patent Literature 1, the movable plate is driven in a floating manner, and so there is a concern that the orientation of the movable plate may be unstable during operation due to being easily affected by fuel flow or gravity.
To deal with this, it is known that the movable plate may be biased by a spring (for example, refer to Patent Literature 2). According to the configuration of Patent Literature 2, a spring is disposed in the back pressure chamber, and by biasing the movable plate, the movable plate may be operated in a stable manner.
However, according to the configuration of Patent Literature 2, the capacity of the back pressure chamber must be increased by an amount corresponding to the installation part of the spring, and if the capacity of the back pressure chamber is increased, the following concerns arise. Specifically, the portions of the injector closer toward the leading side than a seat portion of the needle are not exposed to high pressure fuel when closed. Then, when opened, the portions closer to the leading side than the seat portion are suddenly exposed to high pressure fuel, and the needle may receive a force in the axial direction.
It is known that due to receiving this force, the valve body may shake and adversely affect fuel injection controls. It is further known that the magnitude of this shaking is proportional to the capacity of the back pressure chamber.